Lec 16/17 Flashcards
Function of each lobe
Frontal: skeletal muscle movements
Parietal: somatic sensory cortex
Occipital: vision
Temporal: hearing
Primary motor cortex contain
Cell body of upper motor neurons
Upper motor neurons are part of
CNS
Axons of upper motor neurons will synapse in
Grey matter
Lower motor neurons are
PNS
Project to innervate skeletal muscle
Peripheral pathway consist of — lower motor neuron
1
Axon collateral of lower motor neuron will
Branch out at distal end and each collateral will synapse (neuromuscular junction) with 1 muscle fiber
Neuromuscular junction consist
Axon terminal
Motor end plate on muscle membrane
Schwann cell sheaths
Schwann cell function at NMJ
Secrete chemicals required for formation and maintenance of NMJ
Motor end plate
Specialized region of muscle membrane that contain high concentration of nicotinic ACH receptors
Lower motor neuron will release neurotransmitters (ACH) and
Muscle cell has NACHR
ACH is always excitatory
Nicotinic ACH receptor
Non selective cation channel
NACHR is non selective channel however
Na flow/flux is higher
In result cell will depolarize
ACH in NMJ is always
Excitatory
Muscle cell name
Muscle fiber
Cell membrane of muscle
Sarcolemma
Muscle cell cytoplasm
Sarcoplasm
Modified ER
Sarcoplasmic reticulum
Muscle fascicle
Bundle of fibers
Skeletal muscle
Bundle of muscle fascicle
Epimysium
Connective tissue around skeletal muscle
Perimysium
Connective tissue around muscle fascicle
Endomysium
Connective tissue around muscle fiber
T-tubules
T-tubules are extensions of cell membrane (sarcolemma) that associate with ends of Sarcoplasmic reticulum
Proteins within myofibril
Myosin
Actin
Troponin
Tropomyosin
Titin
Nebulin
Sarcomere
Unit of myofibril between 2 z-disks
Skeletal muscles contain
Organized sarcomeres
Striped or striated
Like cardiac muscle
Striation of skeletal muscle is
Alternation between A band and I band
Myosin
Thick filament
Motor unit create movement
2 intertwined protein chains
Each myosin one actin binding site/one ATP binding site(ATP hydrolyses)
Thick filament= —— myosin molecules
250
Actin molecule
One actin=Globular g-actin
Polymerize to form F-actin
Each G-actin single myosin binding site
Thin filaments
Two chains of F-actin intertwined
Troponin
Trimeric protein
Bind to tropomyosin has 2 cCa binding site
Tropomyosin
Long protein dimer attach to actin
Covering the myosin binding site
— so myosin cannot securely attach
Titin
Huge, elastic, resting length
One Z disk to neighboring M line
Return stretched muscle to resting length
Nebulin
Along thin filaments
Attach z disk but does not reach M line — inelastic molecule
Structural support for thin filament
Molecules required for cross-bridge
Ca ion—enable myosin heads to attach actin by revealing myosin binding site
high-force cross-bridge formation
ATP—bind to myosin and allow it to detach from actin
cross-bridge cycling
Without Ca
-Troponin is inactive
-Tropomyosin partially block myosin
-Myosin can bind to actin only weakly
-Low-force cross-bridge
By increase in [Ca]
-activate troponin
-pulls tropomyosin away from myosin binding site
-myosin bind strongly to actin/complete power stroke
-actin filament moves
Contraction cycle
1- ATP bind to myosin/myosin release actin
2- Myosin hydrolyze ATP
3- Energy from ATP will rotate myosin head
4- Power stroke happen (tropomyosin moves away)
5- myosin release ADP at the end of power stroke
What doesn’t change length
Thick and thin filament
A band
What change length during contraction
I band
H zone
Sarcomere shorten (z line closer)
Excitation-Contraction coupling in skeletal muscle
1- somatic motor neurons release ACh at NMJ
2- net entry of Na from ACH-receptor-channels
3- AP
4- ap move in t-tubule
5- alter conformation DHP receptor
6- DHP open RyR channels in Sarcoplasmic reticulum which are mechanically gated
7- Ca enter cytoplasm
8- Ca bind to troponin
9- allow actin-myosin binding
10- myosin head execute power stroke
11- actin filament move toward centre of sarcomere
Skeletal muscle relaxation (Ca removal)
1- sarcoplasmic Ca-ATPase (SERCA) pumps Ca back into SR
2- decrease free cytosolic Ca
3- Ca unbind with troponin
4- tropomyosin recovers binding site
5- myosin head release
6- titin pull filaments back to their relaxed position
Muscle twitch
One contraction + one relaxation
In a single fiber
Forces in skeletal muscle can
Sum
Summation can lead to
1- unfused tetanus
2- complete tetanus
Unfused tetanus
Allow muscle to relax slightly between stimuli
Complete tetanus
Steady tension
No break
Full capacity
Motor unit
One motor neuron and the muscle fiber it innervate
Size of motor neuron related to
Need of refined movement
More refined movement’
Fewer fibers per motor unit
Order the motor units recruited is related to
Power needed to generate movement
— smaller motor unit recruited first
Smaller motor neuron
Lower threshold for activation
Activate by lower frequency of stimulation from CNS
Sarcomers contract with maximum force when ———
They are in their normal resting length prior to contraction
— optimal number of cross-bridges
